Historically, Internet registries and Internet service providers allocated IP addresses in blocks of for Class C or larger octet-based blocks for classes B and A. By definition, each block fell upon an octet boundary. The structure of the reverse DNS domain was based on this definition. However, with the introduction of Classless Inter-Domain Routing , IP addresses were allocated in much smaller blocks, and hence the original design of pointer records was impractical, since autonomy of administration of smaller blocks could not be granted.
An IPv6 address appears as a name in this domain as a sequence of nibbles in reverse order, represented as hexadecimal digits as subdomains.
For example, the pointer domain name corresponding to the IPv6 address dbab is b. Multiple PTR records are used, for example, when a web server supports many virtual hosts — i.
Postel Ed. The resulting PTR record would look like this: 5. From about , most Generic top-level domain gTLD registries have adopted this so-called thick registry approach, i. No, I am a new user :. Test our caching-only DNS server. Retrieved 25 July Internet Explorer 4.
DNS-Based Service Discovery uses specially-named records in the reverse DNS tree to provide hints to clients about subnet-specific service discovery domains. From Wikipedia, the free encyclopedia. Finding a domain name associated to an IP address. For Java-like naming convention, see Reverse domain name notation. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.
Archived from the original html on 30 March Retrieved 25 July February Retrieved November Huston August Deprecation of "ip6. Using fully qualified domain names FQDNs , instead of IP addresses, to specify network addresses eases the configuration of services and applications, and increases the maintainability of configuration files.
Setting up your own DNS for your private network is a great way to improve the management of your servers. This provides a central way to manage your internal hostnames and private IP addresses, which is indispensable when your environment expands to more than a few hosts. The CentOS version of this tutorial can be found here. To complete this tutorial, you will need the following infrastructure. Create each server in the same datacenter with private networking enabled :.
On each of these servers, configure administrative access via a sudo user and a firewall by following our Ubuntu Refer to the following table the relevant details:. Note Your existing setup will be different, but the example names and IP addresses will be used to demonstrate how to configure a DNS server to provide a functioning internal DNS.
You should be able to easily adapt this setup to your own environment by replacing the host names and private IP addresses with your own. If you utilize multiple datacenters, you can set up an internal DNS within each respective datacenter. By the end of this tutorial, we will have a primary DNS server, ns1 , and optionally a secondary DNS server, ns2 , which will serve as a backup.
Note Text that is highlighted in red is important! It will often be used to denote something that needs to be replaced with your own settings or that it should be modified or added to a configuration file. For example, if you see something like host1. On both DNS servers, ns1 and ns2 , update the apt package cache by typing:.
On both servers, edit the bind9 default settings file by typing:. It should look like the following:. We will start with configuring the options file. This is where we will define a list of clients that we will allow recursive DNS queries from i.
Using our example private IP addresses, we will add ns1 , ns2 , host1 , and host2 to our list of trusted clients:. Now that we have our list of trusted DNS clients, we will want to edit the options block. Currently, the start of the block looks like the following:. Below the directory directive, add the highlighted configuration lines and substitute in the proper ns1 IP address so it looks something like this:. When you are finished, save and close the named. Aside from a few comments, the file should be empty.
Here, we will specify our forward and reverse zones.
Assuming that our private subnet is If your servers span multiple private subnets but are in the same datacenter, be sure to specify an additional zone and zone file for each distinct subnet. When you are finished adding all of your desired zones, save and exit the named. Now that our zones are specified in BIND, we need to create the corresponding forward and reverse zone files. According to our named. We will base our forward zone file on the sample db. Copy it to the proper location with the following commands:.
First, you will want to edit the SOA record. Every time you edit a zone file, you need to increment the serial value before you restart the named process. It should now look something like this:. Next, delete the three records at the end of the file after the SOA record. At the end of the file, add your name server records with the following lines replace the names with your own.
Now, add the A records for your hosts that belong in this zone. Using our example names and private IP addresses, we will add A records for ns1 , ns2 , host1 , and host2 like so:. On ns1 , for each reverse zone specified in the named. We will base our reverse zone file s on the sample db. Copy it to the proper location with the following commands substituting the destination filename so it matches your reverse zone definition :. Edit the reverse zone file that corresponds to the reverse zone s defined in named.
In the same manner as the forward zone file, you will want to edit the SOA record and increment the serial value. It should look something like this:. Now delete the two records at the end of the file after the SOA record. Then add PTR records for all of your servers whose IP addresses are on the subnet of the zone file that you are editing. In our example, this includes all of our hosts because they are all on the Be sure to substitute names and private IP addresses to match your servers:. Save and close the reverse zone file repeat this section if you need to add more reverse zone files.
If your named configuration files have no syntax errors, you will return to your shell prompt and see no error messages. The named-checkzone command can be used to check the correctness of your zone files. Its first argument specifies a zone name, and the second argument specifies the corresponding zone file, which are both defined in named. When all of your configuration and zone files have no errors in them, you should be ready to restart the BIND service.
In most environments, it is a good idea to set up a secondary DNS server that will respond to requests if the primary becomes unavailable. Luckily, the secondary DNS server is much easier to configure. Save and close the named. Define slave zones that correspond to the master zones on the primary DNS server. If you defined multiple reverse zones in the primary DNS server, make sure to add them all here:. Now you must configure your client servers to use your private DNS servers. On Ubuntu To configure DNS, we need to write a Netplan configuration file.